Neways: High Switching Frequency in GaN-enabled PV Inverter

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As System Innovator Neways is working on different innovation projects. One of these projects is the European GaNext project where we are building an Intelligent Power Module (IPM) together with our international partners to remove existing barriers for adopting the Gallium Nitride (GaN) technology for practical solutions. Our share is to build an extremely compact solar inverter (PV inverter) that incorporates both the GaN technology and the IPM to contribute to the miniaturization of power applications.

Therefore, we are using a two stage approach. At first we are building a PV inverter using GaN devices and second we will build a PV inverter using the Intelligent Power Module.

To reduce the size we need to increase the switching frequency. Therefore, we defined requirements and started on the implementation of our PV inverter using GaN devices. Consortium partner Cambridge GaN Devices Ltd. (CGD) provided the 650V GaN components, and other consortium  partner Sumida provided the inductors. The effect of the increased switching frequency is immediately seen: Only two coils of 33 cm3 are well capable of converting the fluctuating solar voltage to a clean DC voltage rail at a power rating of 3 kW. Another set of two coils are used in the transformerless inverter stage. These compact inductors help us in achieving one of the most important targets of this project – a power conversion density of 1 kW/l.

This high power density is only possible due to the high switching frequency. The PV inverter is dimensioned to operate at switching frequencies up to 500 kHz. Although, from technology perspective, GaN is capable of much higher switching frequencies, the switching frequency is a tradeoff between coil losses, switching losses, coil dimensions and many more parameters. 

A large effort was spent to determine the optimum frequency for this application using simulations and calculations. The benefits of an increased frequency are a reduced energy storage and a reduced inductance value, directly influencing the size. But the relative size reduction decreases with increased frequency, and the associated losses increase, as can be seen in the figure below. Based on these parameters an optimum switching frequency can be determined.

About the GaNext project 

Gallium Nitride ”GaN” is a promising material to replace silicon in power electronics application in the 650 V market sector. Power systems based on GaN can be lighter, more compact, significantly more efficient and potentially cheaper than those based on Silicon. Within the GaNext project we aim to remove barriers for GaN adoption and demonstrate the higher efficiency and power density of GaN-based system in a range of applications. The heart of the project is the development of an intelligent GaN power module where the controller, drivers and protection circuits are co-packaged with the power devices.